1. Field of the Invention
This invention pertains to well cleaning tools such as those employed in oil, gas, or water well cleaning operations and more specifically to such tools having a plurality of small scratching elements for independently removing debris from the interior surface of well casings or used in combination with solvents for such purposes.
2. Description of the Prior Art
Oil, gas, water, and other types of wells almost always use casing, a steel pipe, to ensure the integrity of a well borehole. The casing wall is cemented during the completion stage of a drilling operation. This cementing operation leaves cement residue on the casing wall which must be removed before initiating well production. Cleaning of the casing wall is also necessary at intervals during well production when debris and residue, such as oil paraffin and scale, accumulate on the casing wall.
The standard tools used for cleaning casing walls are referred to as casing scrapers and are well known in the art. A typical casing scraper is incorporated in a "plug" and usually incorporates metal blades attached to an elongated body. The blades scrape the casing wall as a hydraulic or mechanical force displaces the body through the casing. A disadvantage of plug-scrapers propelled by hydraulic force is that the scrapers and the debris scoured from the casing wall are not retrievable. The scrapers and debris are displaced to a point past the formation of interest where they remain to clutter the well borehole.
Alternatively in the prior art, a scraper is mounted onto a tool that is attached to the workstring for mechanical manipulation and retrieval once the cleaning operation has been completed. However, a drawback of such scraper tools is that the blades often shear off during cleaning, and a high cost fishing job is required to remove the lost component from the well. Another disadvantage exists in the fact that many common casing scrapers do not achieve 360 degree contact with the casing wall unless they are rotated during the cleaning process. This rotation increases the probability of blades being sheared off the body.
An example of a casing scraper that ameliorates many of these deficiencies of the current technology is disclosed in U.S. Pat. No. 4,896,720. This form of a plug-scraper employs bristles rather than blades, and the entire tool is constructed of easily drillable materials. Therefore, the need for expensive fishing jobs is eliminated. However, neither the tool nor the debris scoured from the casing wall is retrievable under the disclosure in U.S. Pat. No. 4,896,720. Other bushing tools utilizing bristles have been developed. Examples of such tools are disclosed in U.S. Pat. Nos. 1,342,618, 1,855,046, 3,827,492, 4,438,812, 4,501,322, and 4,747,452. Most of these brushing tools are not used in the well cleaning industry because the brushes are not sufficiently stiff nor do they contact the casing wall with sufficient pressure to achieve the same extent of scouring as the scrapers.